1. Field of the Invention
The present invention relates to electrical inductors and transformers. More particularly, the present invention relates to a low profile, high current inductor or transformer including a ferromagnetic core structure having multiple gaps to reduce stray electromagnetic fields.
2. Introduction to the Invention
High current, low profile inductors and transformers are widely used in diverse applications in the fields of telecommunications, power conversion, and digital data circuits. Such electrical components most frequently employ ferromagnetic cores and shields. Ferromagnetic materials such as iron powder, and ferrimagnetic materials such as ferrites (also referred to hereinafter as “ferromagnetics”), have a characteristic temperature below and above which their electromagnetic properties differ greatly. This temperature is known as the Curie temperature. Above the Curie temperature, these materials behave as paramagnetic materials. Below the Curie temperature, these materials exhibit well-known hysteresis B versus H curves. When used as core structures for inductors and transformers, it is essential to keep these materials below the Curie temperature and also to prevent core saturation. One known way to inhibit core saturation of these materials is to provide a gap in a magnetic core structure.
As circuit layouts continue to become smaller and smaller, a hitherto unsolved need has arisen to minimize stray electromagnetic fields associated with inductors and transformers having conductors carrying high currents and carried in two-piece ferromagnetic cores having a gap to prevent core saturation. While magnetic core structures have often been used in high current environments and applications, prior approaches to reduce size and unwanted radiated emissions while carrying ever increasing levels of current have proven to result in structures that were either too bulky in size, too hot in operation, or just too hazardous to use in a particular application or environment.
In a typical electromagnetic device 11 of the prior art as shown in FIG. 1, a single discrete air gap 10 is defined in a two-piece ferromagnetic core structure 12. The gap 10 enables the core structure 12 to handle large amounts of electrical current without saturating. As noted above, once a magnetic core structure saturates, it ceases to operate with its desired inductive capabilities. In practical situations core saturation can result in anything from a simple overload condition to thermal runaway and even catastrophic failure. Although the air gap 10 can usually prevent the magnetic core from saturating, it has an adverse effect on any nearby conductors. A magnetic field (denoted by reference numeral 13) at the air gap 10 effectively reduces the current carrying capability of a conductor 14 because of the well known “proximity effect”. The proximity effect is present when conductors are exposed to strong magnetic fields and exhibit larger than expected resistance to current flow. Increased conductor resistance results in generation of higher levels of heat and can lead directly to thermal runaway and catastrophic failure of the electromagnetic device and/or circuit or appliance including the device.
Examples of gapped core electrical inductors transformers of the prior art are provided by U.S. Pat. No. 4,424,504 to Mitsui et al., entitled: “Ferrite Core”; and U.S. Pat. No. 4,760,366 to Mitsui, entitled: “Ferrite Core”.